Billionaire Tom Steyer on Wednesday night hosted Senate Majority Leader Harry Reid of Nevada and six other Democratic lawmakers for a fundraiser at his San Francisco home and is planning an ad campaign for candidates who support tough action on climate change.

Steyer, founder of the hedge fund Farallon Capital, plans to spend $50 million of his own money and raise another $50 million from other donors for the November midterm elections.

His aim is to serve as a political counterweight to the conservative billionaire Koch brothers, who have already spent $30 million so far this year on attack ads targeting vulnerable Democratic senators who have supported the healthcare reform law popularly known as Obamacare.

Steyer hosted Reid and some of Congress’ most active climate change advocates: Senators Sheldon Whitehouse of Rhode Island, Jeanne Shaheen of New Hampshire, Ben Cardin of Maryland, Patrick Leahy of Vermont, Tom Udall of New Mexico, and Representative Gary Peters of Michigan, according to a source who attended the dinner and who spoke on condition of anonymity.

They were joined by former Vice President Al Gore, who has spent much of his post-Washington life campaigning for strong climate change legislation, such as a carbon tax.

The 40-person dinner, paid for by the Democratic Senatorial Campaign Committee, raised more than $400,000. Democratic donors Mark Buell and Susie Tompkins Buell, co-founder of the Esprit clothing company, and Lorna and Wade Randlett, renewable energy investor and founder of the Bay Area Democrats, co-hosted the dinner of salmon and grass-fed beef from Steyer’s ranch.

KEYSTONE TEST

Steyer used the opportunity to share the latest results of a poll his group released on Thursday that show that American voters are deeply concerned about the construction of the controversial Keystone XL pipeline.

The poll examines “voter sentiments related to whether the TransCanada (Corp.) oil will stay in the U.S. or leave the country; nature of foreign investment; and whether TransCanada should be required to testify under oath as to where the refined oil will go,” said the source who attended the fundraiser.

The poll of 5,000 voters conducted by SurveyUSA found that 85 percent of registered voters want Congress to know whether the Canadian oil being transported by the pipeline will end up overseas, against what NextGen said was a pledge by TransCanada to keep the oil in North America.

Matt Dempsey of the group Oil Sands Fact Check disputed the findings of the NextGen poll and said most Americans favor construction of the pipeline.

“What do you do when you’re clearly on the losing side in your own party? You pay for your own poll that asks misleading questions designed to get the results you want,” he said in a statement.

Steyer has been a vocal opponent of the Keystone XL pipeline and has called on the Obama administration to reject a permit that would allow the project to cross the U.S.-Canadian border.

The pipeline has taken on a wider meaning for Obama, who says he is committed to energy independence and weaning the nation off fossil fuels blamed for climate change.

Steyer’s NextGen group is even willing to challenge vulnerable Democrats who have voiced support for the Keystone pipeline.

Earlier this month, it launched a campaign to get people to vote online for a candidate that NextGen should target in its next TV ad. The list includes newly minted Senate Energy Committee Chair Mary Landrieu, a Louisiana Democrat.

Chris Lehane, a political adviser to Steyer, told reporters that it is not in the interest of a vulnerable candidate like Landrieu to take a strong pro-energy industry stance when “fossil fuel companies are still spending a ton of dough to take you out.”

Lehane said NextGen was looking at 14 possible campaigns to target this election season but said they have not finalized the list.

The group will consider three questions when deciding whether to get involved, he said: Will the climate change issue play a role at the polls; will the state be relevant to the 2016 presidential race or to keeping control of the Senate this year; and will a state pursue a significant climate initiative if a prospective candidate wins?

A New York Times article said the group is looking at a Senate race in Iowa and support for the Democratic candidate, Representative Bruce Braley, an advocate of measures to address climate change.

Steyer may also be considering the governor’s race in Florida and supporting the challenger to incumbent Republican Rick Scott. Scott has said that scientific evidence has not established that humans have caused climate change.